Commercial extraction processes for aromatic hydrocarbon recovery typically involves hydrotreating feedstock in a hydrodesulfurization unit to remove sulfur and nitrogen before undergoing extractive distillation (ED) with a non-aqueous selective solvent to produce a high purity benzene product. For example, U.S. Pat. No. 5,215,629 to Skatulla et al. discloses an ED process that uses non-aqueous N-substituted morpholine solvent to separate aromatics from mixtures containing non-aromatics that entails distilling a raffinate (non-aromatics) stream from the overhead of an extractive distillation column (EDC) in a separate distillation column. U.S. Pat. No. 5,252,200 to Skatulla et al. simplifies the configuration and operation of the '629 patent process by including the feature of distilling the raffinate (non-aromatics) stream from an overhead of the EDC in an internal distillation column that is installed on top of the EDC to recover a selective solvent residue from the raffinate. The distillation column is installed as an integral upper portion of the EDC for recovery of the selective solvent residue from the overhead raffinate stream.
Hydrotreatment of feedstock generates methyl cyclohexane (MCH) through non-selective hydrogenation of toluene. Since MCH is one of the major contaminants in the final benzene product, the hydrodesulfurization (HDS) unit is operated under stringent conditions in order to maintain the required balance between removing sulfur and nitrogen contaminants and minimizing the formation of MCH. Consequently, in order to meet MCH specifications for benzene products, the ED operates under process conditions that result in excessive benzene loss to the overhead raffinate stream and yields lower quality non-aromatic products.